Vehicles may be fitted with evaporative emission control systems to reduce the release of fuel vapors to the atmosphere. Evaporative emissions control systems may include a fuel vapor canister configured to adsorb refueling, diurnal, and running loss fuel vapors. Over the course of one or more diurnal cycles, fuel vapor may become desorbed from the fuel vapor canister. The desorbed fuel vapors may travel to atmosphere, thus comprising emissions and wasting fuel.
Thus, evaporative emissions control systems may include a bleed canister, located between the main fuel vapor canister and the atmosphere, to bind the desorbed vapors. Typical vapor canisters may include a bleed canister inside the vapor canister to reduce diurnal emissions occurring during the inactive state of the vehicle. A large primary carbon bed in the vapor canister handles a majority of the fuel vapors during vehicle use and refueling, and the bleed canister close to the atmospheric vent uses an activated carbon bleed element to capture low concentration hydrocarbon vapors dining the inactive state of the vehicle from being expelled into the environment.
In one of the approaches shown in U.S. Pat. No. 6,896,852, a carbon scrubber for capturing bleed emissions from a vapor canister is mounted outside the vapor canister in a vapor conduit coupling with an atmospheric port of the vapor canister. The carbon scrubber is configured to receive and absorb the bleed emissions from the vapor canister before the vapors are released to the atmosphere through the atmospheric port.
However, the inventors herein have recognized a few issues in the above mentioned approaches. Positioning the carbon scrubber in a separate conduit increases the packaging space of the evaporative emissions control system. Further, the bleed element capacity of the carbon scrubber may be limited and may not be varied to meet more stringent emission requirements. Especially in vehicles with larger fuel tanks, the bleed element capacity may not be adequate to capture all of the bleed emissions efficiently, resulting in degradation of emissions. Further, in vapor canisters that include a bleed element section inside the vapor canister, limited packaging space is available within the vapor canister itself, and therefore, it may be desirable to eliminate the bleed element section inside the vapor canister to allow a larger volume of hydrocarbon trapping material in the primary carbon bed, without compromising on bleed element capacity.
The inventors herein have recognized the above issues and provide an approach to at least partly address them. In one example, a vapor canister includes a first port connecting to a fuel tank, a second port connecting to an engine intake, a third port connecting to atmosphere, and a series of fluidically coupled bleed element shells coupled externally to a sidewall of the vapor canister. The series of fluidically coupled bleed elements includes a first bleed element shell fluidically coupled to the third port through a first flow path passing through the sidewall of the vapor canister and to the first bleed element shell, and a last bleed element shell fluidically coupled to a chamber inside the vapor canister through a second flow path passing through the sidewall into the chamber.
In this way, by providing a series bleed element shells coupled to an outside wall of a vapor canister, adequate bleed emission trapping capacity for capturing bleed emissions from the vapor canister may be provided while preserving additional space inside the vapor canister and without increasing the packaging space of the vapor canister and associated componentry. By integrating the bleed element shells with the vapor canister sidewall and directing fuel vapors and/or fresh air between the bleed element shells and the vapor canister via flow paths within the sidewall, external components and conduits may be minimized, reducing packaging space and cost. Further, the number of bleed element shells that house adsorbent material may be easily adjusted to accommodate relatively small or relatively large expected vapor load on the vapor canister.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.